Acknowledgements

Jon Claerbout gets the award for providing the space, resources, and a great environment to do it. Thanks go to him, S. Fomel, and M. Prucha at SEP, and K. Larner at the Colorado School of Mines for keeping my wording ,spelling, and references honest. W. Symes at Rice, G. Neale in Tulsa, and N. Bleistein at the Colorado School of Mines are also acknowledged for supporting and encouraging completion of this work. Although he probably doesn't know it, P. Fowler showed me the relationship between the various techniques mentioned in the introduction.